Selective catalytic reduction（SCR） technology can effectively effectively solve the problem of NOx non-compliance in iron ore sinter flue gas emissions and achieve ultra-low emissions of waste gases. The uniformity of the physical field distribution such as flow field, temperature, pressure and concentration ratio of ammonia-nitrogen in the SCR reactor are important factors in determining the denitrification efficiency. Based on the low denitrification efficiency and ammonia escape problem in a steel plant, the flow field was numerically simulated using FLUENT software to compare and analyze the values and uniformity of the distribution of each physical field such as flow field, temperature, pressure and concentration ratio of ammonia-nitrogen in the SCR reactor, considering the chemical reactions in the reactor during denitrification. The uniformity of the physical fields is greatly improved by adding a rectifier grille and optimizing the structure of the deflectors, and the denitrification efficiency is improved. After structure optimization, the deviation of flue gas flow rate inhomogeneity upstream of the first layer of catalyst is reduced to 8.48%, the deviation of temperature inhomogeneity is reduced to 4 K,and the deviation of concentration ratio of ammonia-nitrogen inhomogeneity is reduced to 4.71%, which satisfied the design requirements.In addition, the optimization of the deflectors structure should take into account the number, thickness, shape and spacing of the baffles, etc.With the increase of the number of deflectors at the elbow on the flue, the deviation of the flue gas velocity inhomogeneity upstream of the first layer of catalyst is gradually reduced, which effectively improves the uniformity of the airflow distribution in the reactor.